Research On Selective Leakage Protector For Small Current Grounding Power System

In China, power system of 3～66kV mainly is built in the way of small current grounding with characteristics of non-effectively grounded neutral point, reducing the damage caused by single-phase ground. It is easy to make wrong since the ground current is small, weak and fault features, and ambient noise greatly influenced by outside interference when small current grounding system single-phase ground fault. In recent years, many engineers in-depth study on a small lot of ground fault current system, and make a lot of line selection criterions, but it seems work unsatisfactory in the view of results of practical application, which severely restricts the development of intelligent power system. An accurate and reliable method for line selection is urgently proposed with safety in production and gradually improvement the reliability of power supply requirements.This paper analyzes the ground fault characteristics of small current grounding system, respectively, ungrounded systems, impedance grounded neutral point system and the neutral point arc suppression coil grounding system failure characteristic quantities of the zero-sequence studied, focusing on analysis of the grounding system in different zero-sequence voltage and zero sequence current phase relationship. According zero sequence parameters characteristic of this paper, zero-sequence and zero sequence active algorithm reactive power algorithm for small current grounding system fault line, and MATLAB as a platform to build power system model for single-phase ground fault simulation.The device uses 16-bit microcontroller MC9S12XS128MAA as the control center, with processing capability, built-in 12-bit AD converter, simplify peripheral circuits. In order to overcome the problem of zero sequence ground fault characteristic quantity amplitude variation rang and detection difficult problem in the small current system, adding programmable amplifier, improve the detection sensitivity, and expand the detection range. Tests show that this scheme can effectively improve the reliability and sensitivity of device for line selection.